A normal exciter lamp has it's peak output in the infrared region, however as the light output is reasonably white, there is a good deal of light emission in the green region, so a magenta dye track will play, albiet at a lower level than a silvered track. Red LEDs on the other hand are fairly monochromatic (there is not much else emitted other than pure red) so if a red LED light source is used, the magenta dye soundtrack will be effectively transparent to the light, so the modulated output from the solar cell will be very low and distorted.

What Stefan says about solar cells being a current source device is true but I don't think this is a factor in this case. As Gordon points out, all reverse scan Red-LED readers use the standard Dolby preamp circuit which is "almost" a virtual earth (or current) input. There is a small series resistor at the input but I am sure it is closer 100ohms, not the 400ohms as stated by Stephan. Why this resistor is there at all is a bit of a mystery because the solar cell would perform better without it. This is because any resistance in the solar cell output causes a voltage to develop, which then opposes the current trying to escape from the cell, causing non linearity and hence distortion. By loading the cell with a virtual earth, all of the current is extracted from the cell, resulting in excellent linearity and thus very low distortion.

As Gordon also points out, Panastereo optical preamps are true virtual earth or "true current" as he puts it, however AFAIK it is also the only preamp ever manufactured that has a "super-balanced" virtual earth input. Unfortunately the considerable benefits of this design are entirely lost when used with a reverse scan reader because the reader's inferior preamp gets in the way. We are currently (no pun intended) developing a range of super-balanced true virtual earth preamp cards as replacements for the preamps in various reverse scan readers to address this problem.

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Ray Derrick
President
Panalogic Corporation Pty Limited
44 Carrington Road
Castle Hill NSW 2154 Australia
Phone: 61 (0)2 9894 6655 Fax: 61 (0)2 9894 6935

If that "high magenta" track did not have silver redeveloped, a mistake was made at the lab! Traditional analog optical tracks are printed with red and green exposure in the printer and processed with a silver redevelopment step, to produce a track having cyan dye, magenta dye, and silver. The optimum cross-modulation density is slightly different when read with tungsten "white light" than with red LED, so the track has to be optimized for one, with slight sibulant distortion on the other. "High magenta" analog tracks restrict the exposure to the magenta layer and have the silver redeveloped, producing a track that has magenta dye and silver. "High Magenta" tracks optimize at about the same density for both "white light" and red LED readers, so they are the best choice with the mix of readers now in theatres.

Cyan dye analog tracks will NOT have silver, eliminating the need for the complex and wasteful soundtrack redeveloper step in the processing. But a red LED reader is absolutely required for cyan dye tracks, as the signal level on old "white light" readers will be too low.

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John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Research Labs, Building 69, Room 7525A
Rochester, New York, 14650-1922 USA
Tel: 716-477-5325 Cell: 716-781-4036 Fax: 716-722-7243
E-Mail: john.pytlak@kodak.com
Web site: http://www.kodak.com/go/motion

One country cinema owner here told me recently that he had reels of national anthems variously with magenta, cyan (or blue) and silver redeveloped variable density tracks. So I asked him the other day to try playing one of the magenta films on one of his red LED readers and he came back to me today to report the exact same symptoms as the Astor cinema, low level and distorted.

I am wondering if the new prints that the Astor commissioned were somehow simply copies of the orginal films complete with magenta dye tracks.

The consequence of all this of course is that cinemas that regularly play vintage material will not be able to convert to red LEDs. So what are they supposed to do when cyan tracks turn up??

Be amazed! I still don't think it will happen...the conversion to red reader has mostly been a function of new installations and they are on a big decline. As such, depending on whos figures you use...the red reader is only at about 50% of the industry so a full-scale roll-out of cyan would be a disaster.

Those responsible for this red-reader insanity should just give up...it is an inferior method of reproduction...we should ride out film's last years on the conventional optical redeveloped soundtrack and those with LEDs can switch over infrared LEDs (which shouldn't take too long since the red variety have such a short life-span.

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John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Research Labs, Building 69, Room 7525A
Rochester, New York, 14650-1922 USA
Tel: 716-477-5325 Cell: 716-781-4036 Fax: 716-722-7243
E-Mail: john.pytlak@kodak.com
Web site: http://www.kodak.com/go/motion

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Gordon, yes that confirms what I have been told. And of course this is interesting considering that both Dolby and Kodak have current patents for using a red coloured LED to read a cyan dye soundtrack. How two companies can have patents that not only have such obvious prior art but also which claim essentially the same thing makes you wonder who they've got working down there at the US patent office. It sure as hell ain't Albert Einstein.